The point being that we are actively working on improving the overall state of documentation. However, if you wish to learn more about the internals, how to some more advanced stuff like writing plugins, building your own stack, knowing when to use what component, I would suggest you attend the training class that Yehuda Katz (Merb lead developer) and myself are giving in Phoenix, AZ, January 19-21.

This would give you a rare opportunity to spend time with some of people directly involved with the day to day development of the framework as well as other like minded developers.